Ever increasing use of mm-wave frequencies in communication systems, particularly those with high data rate, requires efficient antennas. Antenna directivity and radiation efficiency has to be reasonably high to overcome the high free space losses at mm-wave frequencies.
Highly efficient planar radiating elements can have various applications. They can be used as the radiating elements on an array, particularly of electronically steered type. In cases where high gain radiators are required, they can be used as the feeding element of a non-array antenna such as a horn or reflector antenna to avoid considerable feed losses, e.g. such as in mm-wave. Millimeter- and submillimeter-wave devices often utilize integrated circuits combined with waveguide components. This requires transitions between waveguides and different planar transmission lines. In addition, transitions to waveguide measurement systems are often needed for device characterization and testing. Efficient planar radiating elements can be tuned for such applications.
U.S. Pat. No. 4,825,220 (Edward et al.) discloses a planar antenna that provides wide bandwidth. FIG. 1 illustrates the planar antenna. Referring to FIG. 1, the structure utilizes a two-layer configuration that is a drawback in terms of manufacturing. Furthermore, the VSWR is not very low and the gain is not high.
Another prior art antenna, depicted in FIGS. 2A and 2B, is the uniplanar Yagi-like type, which consists of two dipole elements, a truncated ground plane and a microstrip-to-coplanar strips (hereinafter the term “coplanar strips” is abbreviated “CPS”) balun. The two dipole elements include a director and a driver. The director and driver of the antenna are placed on the same plane of the substrate so that the surface waves generated by the antenna are directed to the end-fire direction.